POS0679 COMPARISON OF ESTABLISHED AND NEW, PRELIMINARY PROPOSED ASAS CUT-OFFS FOR INFLAMMATORY MRI LESIONS IN THE SACROILIAC JOINTS OF AXIAL SPONDYLOARTHRITIS PATIENTS AND IMPLICATIONS FOR RECRUITMENT IN CLINICAL STUDIES
Authors: X. Baraliakos, P. Machado, L. Bauer, B. Hoepken, M. Kim, T. Kumke, R. Tham, M. Rudwaleit
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> The Assessment of SpondyloArthritis international Society (ASAS) recently proposed preliminary, more stringent, data-driven definitions for active and structural MRI lesions of the sacroiliac joint (SIJ) typical of axial spondyloarthritis (axSpA) <sup>[1]</sup>. <h3>Objectives</h3> To assess clinical outcomes of patients (pts) receiving certolizumab pegol (CZP) in the C-OPTIMISE trial who were MRI-positive (MRI+) or negative (MRI–) according to the existing and newly proposed definitions, as well as those who were MRI+ by the existing definition but MRI– by the newly proposed definition (discordant group). <h3>Methods</h3> C-OPTIMISE (NCT02505542) enrolled 736 pts with active axSpA who received 400 mg CZP at Weeks 0, 2, and 4, then 200 mg CZP every two weeks to Week 48 <sup>[2]</sup>. We report: percentage of pts achieving ASAS ≥40% improvement (ASAS40) response; mean BASDAI change from baseline (CfB) and percentage of pts achieving Ankylosing Spondylitis Disease Activity Score (ASDAS) inactive disease (ID, ASDAS &lt;1.3) to Week 48. In this post hoc analysis, outcomes were stratified by axSpA subgroup (radiographic [r-]/ non-radiographic [nr]-axSpA) and MRI definition. Missing values were imputed using non-responder imputation for ASAS40 and last observation carried forward for continuous variables. <h3>Results</h3> Baseline MRI data were available for 657/736 (89.3%) pts, 358/657 (54.5%) of whom had r-axSpA and 299/657 (45.5%) nr-axSpA. 386/657 pts (58.8%) were classified as MRI+ according to the existing definition compared with 333/657 pts (50.7%) using the newly proposed definition; the discordant group comprised 53/657 pts (8.1%; nr-axSpA: 35/299 [11.7%]; r-axSpA: 18/358 [5.0%]; <b>Table 1</b>). A numerically higher proportion of newly proposed definition MRI+ pts achieved ASAS40 at Week 48 vs those fulfilling the existing MRI+ definition; pts in the discordant group responded similarly to those originally classified as MRI– (<b>Figure 1</b>). Similar results were observed for mean BASDAI, with significant differences in responses between nr-axSpA pts in the newly proposed MRI+ definition and discordant groups (<b>Figure 1</b>). At Week 48, a lower proportion of pts in the discordant group achieved ASDAS inactive disease (ID, ASDAS &lt;1.3) vs those classified as MRI+ according to either the existing or newly proposed definitions; differences between subgroups were more notable among pts with nr-axSpA (discordant group: 15/35 [42.9%]; existing definition MRI+: 112/191 [58.6%]; newly proposed definition MRI+: 97/156 [62.2%]) than with r-axSpA (discordant group: 10/18 [55.6%]; existing definition MRI+: 118/195 [60.5]); newly proposed definition MRI+: 108/177 [61.0%]). <h3>Conclusion</h3> In C-OPTIMISE, 11.7% fewer nr-axSpA pts would have been classified as MRI+ at baseline using the newly proposed definition vs the existing definition. Application of the preliminary MRI definition needs to be evaluated in future clinical trials to confirm its translation into fewer false-positive recruited pts. <h3>References</h3> [1]Maksymowych WP. Rheumatology 2021;60(10):4778–89. [2]Landewé RB. Ann Rheum Dis. 2020;79(7):920–28. <h3>Acknowledgements</h3> This study was funded by UCB Pharma. Medical writing support was provided by Costello Medical, funded by UCB Pharma. <h3>Disclosure of Interests</h3> Xenofon Baraliakos Speakers bureau: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer and UCB Pharma, Paid instructor for: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer and UCB Pharma, Consultant of: AbbVie, BMS, Chugai, Eli Lilly, Galapagos, Gilead, MSD, Novartis, Pfizer and UCB Pharma, Pedro Machado Consultant of: AbbVie, BMS, Celgene, Eli Lilly, Galapagos, GSK, Janssen, MSD, Novartis, Orphazyme, Pfizer, Roche and UCB Pharma, Grant/research support from: Orphazyme, Lars Bauer Shareholder of: UCB Pharma, Employee of: UCB Pharma, Bengt Hoepken Shareholder of: UCB Pharma, Employee of: UCB Pharma, Mindy Kim Shareholder of: UCB Pharma, Employee of: UCB Pharma, Thomas Kumke Shareholder of: UCB Pharma, Employee of: UCB Pharma, Rachel Tham Employee of: Veramed statistical consultant for UCB Pharma, Martin Rudwaleit Speakers bureau: AbbVie, Boehringer Ingelheim, Chugai, Eli Lilly, Janssen, Novartis, Pfizer, and UCB Pharma, Consultant of: AbbVie, Eli Lilly, Novartis, and UCB Pharma.